Insulin, the major metabolic hormone for the regulation of glucose homeostasis, mediates its action by reducing hepatic glucose output and by increasing the rate of glucose uptake by skeletal muscle and adipose tissue (M. Bliss, Univ. of Chicago Press, 1982). Glucose uptake into muscle cells and adipocytes by insulin is carried out by the glucose transporter GLUT4. Some insulin-related metabolic disorders are insulin resistance, diabetes mellitus and metabolic syndrome.
Insulin resistance is the condition in which insulin, even though present in normal amounts, is unable to produce a normal insulin response from fat, muscle and liver cells. Insulin resistance in fat cells leads to increased hydrolysis of stored triglycerides and increased mobilization of stored lipids, which in turn, elevates free fatty acids in the blood plasma. Insulin resistance in muscle cells reduces glucose uptake and local storage of glucose as glycogen, whereas insulin resistance in liver cells reduces storage of glycogen, making it unavailable for release into the blood when blood insulin levels fall. High plasma levels of insulin and glucose due to insulin resistance often lead to metabolic syndrome and type 2 diabetes, including its complications.
Diabetes affects over 18.2 million people in the United States, representing over 6% of the population. Diabetes is characterized by the inability to produce or properly use insulin. Diabetes type 2 (also called non-insulin-dependent diabetes or NIDDM) accounts for 80-90% of the diagnosed cases of diabetes and is caused by insulin resistance. Insulin resistance in diabetes type 2 prevents maintenance of blood glucose within desirable ranges, despite normal to elevated plasma levels of insulin. Additionally, glucotoxicity, which results from long-term hyperglycemia, induces tissue-dependent insulin resistance (Nawano et al., Am. J. Physiol. Endocrinol. Metab., 2000, 278, E535-543) exacerbating the disease. Chronic hyperglycemia is also a major risk factor for diabetes-associated complications, including heart disease, retinopathy, nephropathy and neuropathy.
Diabetes and obesity (sometimes collectively referred to as “diabesity”) are interrelated in that obesity is known to exacerbate the pathology of diabetes and greater than 60% of diabetics are obese. Most human obesity is associated with insulin resistance and leptin resistance. In fact, it has been suggested that obesity may have an even greater impact on insulin action than diabetes itself (Sindelka et al., Physiol Res., 2002, 51, 85-91). Additionally, several compounds on the market for the treatment of diabetes are known to induce weight gain, a very undesirable side effect to the treatment of this disease.
Cardiovascular disease is also interrelated to obesity and diabetes. Cardiovascular disease encompasses a wide variety of etiologies and has an equally wide variety of causative agents and interrelated players. Many causative agents contribute to symptoms such as elevated plasma levels of cholesterol, including non-HDL cholesterol, as well as other lipid-related disorders. Such lipid-related disorders, generally referred to as dyslipidemia, include hypercholesterolemia and hypertriglyceridemia among other indications. Non-HDL cholesterol is firmly associated with atherogenesis and its sequalea, including cardiovascular diseases such as arteriosclerosis, coronary artery disease, myocardial infarction, ischemic stroke, and other forms of heart disease. These rank as the most prevalent types of illnesses in industrialized countries. Indeed, an estimated 12 million people in the United States suffer with coronary artery disease and about 36 million require treatment for elevated cholesterol levels.
Metabolic syndrome is a combination of medical disorders that increase one's risk for cardiovascular disease and diabetes. The symptoms, including high blood pressure, high triglycerides, decreased HDL and obesity, tend to appear together in some individuals. It affects a large number of people in a clustered fashion. In some studies, the prevalence in the USA is calculated as being up to 25% of the population. Metabolic syndrome is known under various other names, such as (metabolic) syndrome X, insulin resistance syndrome, Reaven's syndrome or CHAOS.
With the high prevalence of cardiovascular disorders and metabolic disorders there remains a need for improved approaches to treat these conditions; including reducing unwanted side-effects.